This invention relates to an all-solid type secondary cell which can perform electric charging and electric discharging
A secondary cell can be charged even after its discharging to use it again and repeatedly. There have been conventionally known secondary cells as a lead storage battery and an alkali storage battery. Recently, a nickel-cadmium battery or a lithium secondary cell has been developed to meet the requirements of small-type or portable-type.
A secondary cell is basically constituted of a positive electrode, an electrolyte layer and a negative electrode. The electrolyte layer is constituted of an electrolyte solution. The electrolyte solution is prepared by dissolving electrolyte such as lithium perchlorate in an organic solvent such as propylene carbonate. A secondary cell composed of an electrolyte solution has such defects in durability as caused by solution leakage or decomposition of electrolyte.
As an effective means to overcome above-mentioned defects caused by an electrolyte solution, it has been proposed to apply solid electrolyte to a secondary cell (for example NIKKEI NEW MATERIALS page 33-page 45, Aug. 11, 1986).
There is proposed an electrolyte layer constituted of solid electrolyte (hereinafter referred to as "a solid electrolyte layer") wherein inorganic materials such as lithium silicate lithium phosphate (Li.sub.3.6 Si.sub.0.6 P.sub.0.4 O.sub.4) are utilized, or lithium trifluoro methane sulfonate etc. is dispersed in polymeric thin layer such as polyethlene oxide, for the formation of the solid electrolyte layer. Solid electrolyte does not give rise to the problem of solution leakage and makes it possible to form a thin electrolyte layer. The application of polymeric thin layer to a solid electrolyte layer advantageously makes it possible t prepare a paper-like and light secondary cell excellent in flexibility and processing characteristics.
Solid electrolyte layer as above mentioned brings about such troubles that the layer is poor in durability because it is liable to absorb water and being subjected to oxidizing; initial properties, even if being excellent, are deteriorated by the repetition of charging-discharging process; electrical conductivity is about 100-10000 times lower than that of a electrolyte solution of lithium etc. The fact is that various researches and developments about new solid electrolyte are actively in progress for the practical use.